Hybrid Force/Position Control Strategy for Electromagnetic based Robotic Polishing Systems

Abstract

Precise control of contact force online is essential to ensure the operation accuracy such as robot polishing, grinding, etc. In this paper, an electromagnetism based compliant polishing device was designed, and a force control strategy based on PD and BP neural network was also proposed. Firstly, the feasibility of the electromagnetic driving strategy of voice coil motor was discussed. By controlling the position using the robot and controlling contact force using the compliant device, the force and position were decoupled. Secondly, the mathematical model of the compliant mechanism was derived. Moreover, in order to improve the dynamic performance of the compliant device and its closed-loop control accuracy, the non-linear load disturbance was compensated by feedforward-control, and the PD (proportional-differential) parameters were optimized by the BP neural network. Furthermore, the system is simulated in MATLAB. The simulation results show that the BP-PD method is better than the conventional PD control with a smaller error. Finally, the experimental platform has been built for polishing. The experimental results demonstrated that the force control strategy could realize the constant force polishing, compared to 0.545\mu m mean roughness of non-force control operation, a superior polishing quality is obtained by force control method with the surface roughness decreased to $0.185\mu m$. Thus, it can be proved that the hybrid force/position control strategy for robotic polishing based on the electromagnetic drive is effective.